This is an application for partial funding to support the fourth in a series of FASEB summer research conferences on the biology of the gastrointestinal (GI) tract. These conferences have been held biannually have been remarkably successful. The scientific focus of each meeting has differed; however, a constant objective has been and remains to bring established investigators together with young scientists and trainees to confer on topics at the frontiers of GI research. Another goal of the proposed meeting is to draw the attention of GI investigators to relevant insights derived from research in related disciplines to which they might not otherwise be exposed. The meeting will be held in the informal surroundings of the Copper Mountain ski resort in Colorado, taking advantage of economical off-season rates, which make it possible for both young and established scientists to attend with a minimum of financial aid. The pleasant setting also facilitates interactions between participants, so that ideas raised during formal sessions will be pursued during social activities. The need for this conference, as well as its topic, Gastrointestinal Tract IV: Development and Repair-Cellular and Molecular Aspects were agreed upon by an overwhelmingly positive vote of the participants at the end of the previous conference (Gastrointestinal Tract III) at Copper Mountain in July, 1989. The focus was enthusiastically greeted as exciting and directed to the advancing front of modern research in the field. It was of interest to all, either because it related to their own current work in progress or because it was of educational value for research they wished to do in the future. An added benefit, realized in the previous conference that should be even more evident in the next, is that attending cellular and molecular biologists gain from their contact with GI scientists an appreciation and insight into the integration and regulatory functions that determine higher levels of behavior of a whole organ. Funamental advantages thus accrue both for clinical gastroenterology and basic research. Objectives will be achieved, in part, by holding sessions on: (1) Stem Cells and Development (Renewal of Epithelium); (2) Cell and Region-Specific Regulation of Intestinal Epithelial Gene Expression; (3) Models of Epithelial Differentiation; (4) Development and Maintenance of Polarized Epithelial Cell Function; (5) Endocytosis and Transcytosis in Mucosal Immunity; (6) Extracellular Modulation of Gastrointestinal Cell Differentiation; (7) Cell Migration and Repair of the Epithelium; (8) The Neural Crest and Gastrointestinal Development; (9) Intestinal Inflammation/Anaphylaxis and Neural Function. Several sessions will be supplemented discussants, who will be forewarned about the speakers presentations and who will be prepared to begin discussion and to introduce controversial aspects of their topics. Poster summaries by young investigators and informal conversations during group dining, afternoon recesses, and socialization after evening sessions will contribute to maximizing interactions among participants.